Whenever you grub-mkfont is used to convert truetype fonts to PFF2 fonts, it
generates several errors. For example:
grub-mkfont -v -s 12 -r 0x0-0x7F -o ~/Documents/dejavu-sans-12.pf2
/usr/share/fonts/truetype/ttf-dejavu/DejaVuSans.ttf
gives the following error:

It's not errors. Just warnings that the resulting pf2 will be of lesser quality
than source TTF

This is a long-standing issue with grub-mkfont that started somewhere in the
later releases of 1.98. This never occurred in earlier releaes of 1.98.